Glow cathode



Patented July 26, 1938 PATENT QFFEQE.

GLOW CATHODE Werner Espe, Berlin-Siemensstadt, Germany, assignor to Siemens-Scliuckertwerke Aktiengesellschaft, BerlimSiemensstadt, Germany, a corporation of Germany Application April 14, 1937, Serial No. 136,875 In Germany July 1, 1936 4 Claims. (01. 250-275) This invention relates to cathodes and especially to cathodes utilizing a large supply of electron emitting material. I

An object of the invention is to provide a cathode containing a large supply of electron emitting material and yet one in which the electron emitting material evaporates with sufficient stability without the formation of ignition or torch spots.

Other objects and advantages of the invention will be apparent from the following description, in which:

Figure l is a cross-sectional view through a preferred form of a cathode constructed according to the invention;

Fig. 2 is a side elevational view of the wire network of Fig. 1;

Figs. 3 and 4 are cross-sectional views of modifications of Fig. l; and

Fig. 5 is a side view partly in elevation and partly in cross-section of the fastening of the lead to the cathode body.

One of the difficulties with the coated cathodes of the prior art is that if a large quantity of electron emitting material is utilized, the rate of electron emission is apt to be very unstable. Thereispresentthe danger of certain parts igniting into a flame with the consequent destruction of the cathode. Even if the cathode does not ignite, yet there is danger of the cathode having an unusually large emission beyond that desired at first due to the large amount of material present.

According to the present invention, the cathode is constructed by providing a plurality of wires, preferably parallel, as supporting cores for the cathode construction. Each of these wires is preferably individually wound with the spiral of thin wire, and then, in addition, the whole assembly is preferably wound with a common wire spiral which holds the whole bundle of wires together. In this manner, a rigid wire network is formed for the electron emissive material. Since each of the core wires is individually Wound with a thin spiral wire, hollow spaces result which can hold a sufficiently large mass of oxides or compounds which may be converted into oxides. There are also intermediate spaces through which the light metals resulting from the oxides and effecting electron emission may diffuse from the inner portion of the wire network to the surface of the cathode. These light metals are generally barium and strontium from the well known barium and strontium oxide coating. In particular, the oxide mass in the intermediate spaces between the wires is rigidly held against any damage from the exterior of the cathode and due to the protecting wires, the ignition of a portion of the exterior coating isprevented.

For the core wires, a material is preferably selected which combines a high specific resistance with a large rigidity so that the cathode assembly does not bend under the influence of its own weight at high temperatures. For the supporting core wires, material from the tungsten group, such as tungsten or molybdenum, or an alloy of both is preferable. For the winding of the individual core wires, a material is utilized to which the oxide mass sticks well, as, for example, copper, or any of the copper group of metals. For the material of the wire for a common winding of the bundle of cores, a material of high solidity is particularly suitable, as nickel.

It is also preferable to provide an additional wire within the oxide coating, and preferably in the center of the core wires or adjacent thereto, of one or more Wires of a material that exert a reduction effect on the electron emitting coating which is, of course, preferably of alkaline earth oxides. This wire, which need not be in conductive connection with the other wires, may consist of some metal such. as magnesium or aluminum. Due to the presence of this wire and its effect upon the coating, an increase in admission is obtained in a very simple manner.

The value of the heating current determines the preferred number of core wires which are preferably three or more. It is preferred that wire material of the same thickness be utilized for the different cathodes, to provide an extensive standardization in manufacture.

In Figure 1, the numeral l identifies the core wires while the thin wires 2 are individually wound thereabout. Numeral 3 is the rigid wire bindings by which the Whole bundle is held together. The spaces t and 5 are filled with electron emissive material previously mentioned. This emissive material is pressed together and held rigidly, especially in the space 4 between the core wires. By reason of the winding of the core wires, there are between them intermediate spaces through which the electron emitting ma terial can in spite of its high compression travel outwardly very freely. Fig. 2 shows the construction of the cathode in side elevation in which the electron emissive material and a por-' tion of the outer Winding are omitted to more clearly illustrate the construction of the wire network.

Fig. 3 shows a modification in which a wire 6 g is embedded in the'oxide mass and this wire may consist of a metal preferably aluminum. Between the aluminum wire and the alkaline earth oxide, a so-called alumino-thermic action takes place whereby the emitting properties of the cathode are very much improved.

Fig. 4 illustrates a further example in which five core wires l are utilized in combination with two aluminum wires 6. The number of wires may be increased in any desired manner in accordance with this relationship. In Figs. 3 and 4, the windings about the core wires are also designated with the numeral 2 and. the common winding of the wire bundle by the numeral 3.

The windings of the wires are made more narrow at the terminals since the wires may be more rigidly held together at this place. In Fig. 5, the cathode conductor 1 is reduced to a pin 8 at its center which is thrust in between the core wires I. It is preferable to thrust the shell 9 over this connecting region. The shell is connected to the cathode or the cathode conductor at the points I and I I by welding. In place of this, the outer winding of the wire bundle may be continued over a predetermined length of the lead wire or at the terminals a second winding may be brought on which encloses the whole wire to attain a high rigidity.

Further, it is advantageous not to cover the terminals of the wires with alkaline earth oxide, but instead the terminals may be coated with a material which radiates heat poorly, such as, for example, aluminum oxide.

The cathodes constructed in accordance with the invention have high stability, good emission properties and long life.

While in accordance with the patent statutes I have disclosed preferred embodiments of my invention, it is apparent that many modifications may be made without departing from the spirit of my invention. Accordingly, I desire only such limitations on the following claims as are necessitated by the prior art.

I claim as my invention:

1. A cathode for electron discharge devices comprising a plurality of core Wires and a coating of alkali earth material thereon, one of said wires being of a material which exerts a reduction efiect on said alkali earth material.

2. A cathode for electron discharge devices having heating current applied thereto comprising a plurality of supporting co-re wires, a wire around each of said supporting core wires, a wire surrounding both sets of wires and an electron emitting material coating on said Wires.

3. A cathode for electron discharge devices comprising a plurality of supporting core Wires, a wire around each of said supporting core wires, a wire surrounding both sets of Wires, an alkali earth material coating on said wires and an additional wire within the coating on said wires of a material which exerts a reduction effect on said alkali earth material.

4. A cathode comprising a bundle of longitudinally extending wires and a connector for one end thereof, said connector having a pointed projection inserted in said bundle and making contact thereto.

WERNER ESPE. 

